超深井套管三维弹塑性ABAQUS有限元分析

针对一个井深为7500 m的竖直油井套管地层中有若干段蠕变严重的盐岩层，在固井后，由于盐岩层蠕变对套管产生的压力引起套管产生过量塑性变形，进而被挤毁。工程单位要求对原设计方案进行三维有限元模拟验算，并要求依据所拥有的资料提出新的设计建议。为此，应用ABAQUS有限元软件对原设计方案进行了三维弹塑性数值分析，进一步对壁厚增加以后的套管进行了弹塑性数值模拟分析。计算内容有：①原设计外径为0.34 m、内径为0.31 m的套管在内外液体压力以及对称的15°扇形区盐岩压力作用下的三维弹塑性分析；②新设计建议外径为0.35 m、内径为0.315 m的套管在内外液体压力和非对称的15°扇形区盐岩压力作用下的三维弹塑性分析；③将上述②的模型所处位置深度增加，即平移使其顶部深度达到6500 m时套管的三维弹塑性分析。结果表明，原设计套管厚度不能承受盐岩层所产生的较大压力梯度，而壁厚增加以后的套管设计承载能力能够满足工作环境要求。

ABAQUS FEM ANALYSIS FOR ELASTOPLASTICITY OF CASING USED IN ULTRADEEP WELLS

The object investigated here is the casing of a vertical well of 7500m deep. Along the depth of wellbore there were several gypsum sections, the serious creeping of which exerted pressure on the casing, resulting in excessive plastic casing deformation and final collapse. It was required to carry out a 3D FEM simulation of the previous casing design, and recommend a new casing design. 3D elastoplasticity numerical analysis was done for the old casing design using ABAQUS FEM software and for the casing with wall thickness increased. The simulation calculation included: ①FEM elastoplasticity analysis of the previously designed casing with OD 0.34m and ID 0.31m under equal internal and external hydraulic pressures and under the compression of the gypsum rocks in symmetric 15°sectors; ②FEM elastoplasticity analysis on the enhanced casing of 0.35m OD and 0.315m ID under internal and external hydraulic pressures and under the compression of the gypsum rocks in asymmetric 15°sectors; ③FEM elastoplasticity analysis on the enhanced casing in ②with well depth increased to 6500m. Results indicate that previous design cannot resist the rather high pressure caused by gypsum layers, and the performance of new design can meet the needs of safety under given working environment.